The present invention relates to an electronic component functioning with reflected acoustic waves on a substrate, said substrate having a reflector structure having finger weighting associated therewith.
A surface wave filter designed as a dispersive delay line and an improvement relating to such a filter are disclosed in German Patent application No. P 31 21 516.5, corresponding to U.S. Ser. No. 377,466, now U.S. Pat. No. 4,427,954; Nos. P 32 09 948.7; and P 32 09 962.2, all incorporated herein by reference. Particularly in the case of the above cited second and third applications, an electronic component functioning with acoustic waves is provided whereby the finger weighting employed to achieve a specific, prescribed transfer function is achieved such that a spacing of finger groups from one another and/or of individual fingers from one another is varied relative to a position of the fingers which would correspond to such a component without finger weighting. In the first cited patent application this finger weighting is realized by means of finger length weighting fundamentally known per se. The non-equidistant spacings of fingers or finger groups from one another in this component serve to achieve a prescribed dispersion of said component.
The invention of the German application No. P 32 09 962.2 offers the advantage (apart from a dispersion realized in this component) of providing the finger weighting necessary for the prescribed amplitude function of the transfer characteristic such that the active portions of the individual fingers of the respectively employed digital structure (structures) extends over the entire width of the working area of the electronic component, i.e. over the entire width of the structure (structures) at right angles relative to the primary propagation direction of the acoustic wave. Despite the presence of a finger weighting, disruptive side effects which are connected with finger length weighted structures or with finger dot weighted structures should be avoided.
In the extreme case, given an electronic component according to German application No. P 32 09 962.2, a shift of respectively adjacent fingers relative to one another can be provided in order to realize the necessary finger weighting (related to a non-weighted structure), i.e. a respective finger group to be subjected to finger weighting consists of only two fingers. Thus, maximum band width is achieved for a structure or for a component according to this earlier invention.
In co-pending U.S. Ser. No. 520,418, a finger weighting for an electronic component functioning with reflected acoustic waves is provided which (just like the finger weighting according to the earlier invention of the application No. P 32 09 962) is free of disruptive side effects, and nonetheless allows the greatest possible (in comparison to a component without finger weighting) or even greater band width in comparison to the system in application No. P 32 09 962.
Given an electronic component as previously described in Ser. No. 520,418, the fingers of the reflector structure to be weighted are functionally divided at least once in their longitudinal direction so as to create sub-fingers. The sub-fingers are offset relative to one another in a primary wave propagation direction by a dimension corresponding to a prescribed weighting.
The invention in Ser. No. 520,418 is based on the consideration that even greater band width of the respective digital structure or of the entire component can only be achieved in comparison to the earlier invention by following a relatively different solution. For this different solution, one can begin with a known electronic component functioning with acoustic waves and, for example, from a component of the earlier application No. P 31 21 516 as well which exhibits varied finger spacings for the realization of a dispersion.
The invention in Ser. No. 520,418 is based on the idea of providing a "finger displacement" which will already influence the individual fingers or the respective individual finger as a finger weighting. The underlying principle of this solution consists of dividing the respective individual finger to be subjected to a finger weighting in a corresponding structure of the electronic component at least once in the longitudinal direction of the finger and to position the at least two parts which have arisen parallel to the primary wave propagation direction in offset manner relative to one another. The primary wave propagation direction is the intended direction in which the acoustic wave proceeds in the electronic component. Given a component with 180.degree. reflection, this is usually a single direction. Given a component with wave reflection differing from 180.degree., for example having 2.times.90.degree. wave reflection (with reflection fingers placed obliquely at an angle of 45.degree.), one primary wave propagation direction then exists which is traversed in the forward direction and parallel thereto in the return direction and a further primary wave propagation direction exists which runs at right angles thereto. Given the latter design of the electronic component, the offset of the finger parts can be realized parallel to one primary wave propagation direction or to the other primary wave propagation direction, or partially to the one and partially to the other primary wave propagation direction. The longitudinal direction of said fingers mentioned in conjunction with the division of the individual fingers is the direction of the largest geometrical dimension of the individual fingers. Given a component with 180.degree. reflection, this longitudinal direction of the finger is usually orthogonal relative to the primary wave propagation direction. Given a component with a bent path of the wave propagation of the acoustic wave, the longitudinal direction of the corresponding finger given, for example 90.degree. reflection in the component, usually proceeds at an angle of 45.degree. relative to the one and to the other primary wave propagation direction (homogeneous or isotropic conditions assumed).